Packages for and methods of packaging medical devices are numerous. The choice of method for packaging a device depends in part on the intended use of the device. Factors include whether the device is used in a sterile environment, whether the device is used in contact with or inserted into a living animal, whether the device is disposable, etc. Certain devices must be sterilized prior to use. One known method for packaging a sterile device is to first insert the device into a gas-impermeable wrap. The interior of the wrap, including the device, is then sterilized. The wrap is then sealed so that the device remains sterilized until the package is opened just prior to use. Once the package is opened, a minimum amount of handling is desirable to avoid the possibility of contaminating the device.
Certain medical devices additionally require calibration prior to use. Medical devices that monitor analyte levels, temperature, etc., often include chemical or electrical sensing components that are very sensitive to temperature, moisture, etc. These devices are generally used in conjunction with monitoring instrumentation that controls and records the monitoring process. For example, a medical device may be connected to a computerized controller which initiates and transmits an electrical or optical signal to the device, receives a resultant signal from the device, and analyzes the resultant signal to produce a value indicative of the measured characteristic.
One common way of calibrating a medical device used for monitoring analyte concentrations is to immerse the sensing component of the device into a calibration solution containing a known amount of the targeted analyte. Base measurement levels are recorded in accordance with the known amount of the analyte. Such calibration solutions must be highly uniform to provide consistent and useful results in the calibration process. The solutions are typically unstable and are only prepared as needed or prepackaged in glass ampules. Glass ampules require especially careful handling during the calibration process to avoid breakage. Shelf life problems, e.g., change of chemistry, separation, etc., may be encountered with prepackaged solutions that are stored over a period of time prior to use. Conventional calibration procedures are time-consuming, costly, subject the device to possible contamination, and often require the presence of a trained technician to oversee the process. Additionally, if a calibratable device is to be stored over a period of time, the device is most easily stored in a dry state to avoid problems arising from the storage of a moist device. Bringing the sensing component of the device from a dry to a functional state often requires hydrating the sensing component over an extended period of time.
When a device must be sterilized as well as calibrated, additional problems arise due to the fact that the sterilization and calibration procedures are often incompatible. For example, one common method of sterilizing a medical device is to expose the device to ethylene oxide (ETO). The ETO procedure is carried out in a non-liquid, i.e., dry, environment. This dry state renders the sensing component of the device completely nonfunctional if the component is meant to operate in a moist environment. In contrast, as discussed above, the common method of calibrating such a device is to immerse the device in a calibration solution. Thus, an ETO sterilization procedure and a moist calibration procedure must be distinct phases in the preparation of the device.
In recent years, optical fiber sensors, also known as optrodes, have been developed to detect the presence of and to continuously monitor the concentration of various analytes, including oxygen, carbon dioxide, glucose, inorganic ions, and hydrogen ions, in solutions. An example of such a sensor is a blood gas sensor for monitoring pH, pCO.sub.2, or pO.sub.2. Such a blood gas sensor is based on the recognized phenomenon that the absorbance or luminescence of certain indicator molecules is specifically perturbed in the presence of certain analytes. The perturbation in the absorbance and/or luminescence profile is detected by monitoring radiation that is reflected or emitted by the indicator molecule when it is in the presence of a specific analyte. The targeted analyte is generally a part of a solution containing a variety of analytes.
Optrodes have been developed that position an analyte-sensitive indicator molecule in the light path at the end of one or more optical fibers. This fiber unit is often termed the sensor component. The sensor component is an integral part of a blood gas catheter. The indicator molecule is typically housed in a sealed chamber at the end of the fiber(s). The chamber is secured to the optical fiber by a suitable cement material. The walls of the chamber are permeable to the analyte. The sensor component is inserted into and left in a patient for an extended period of time. Analyte readings in the form of optical signals are transmitted from the sensor component to monitoring instrumentation which analyzes the signals and controls the monitoring process.
The sensor component in a blood gas catheter thus typically includes a membrane material, an analyte sensing material, an optical fiber, and a cement. Each element is chosen to be compatible with the other elements and with the monitoring process. In order to monitor a specific analyte, the sensor component is sterilized and then brought to a functional state in which the catheter sensor is responsive to the targeted analyte. Additionally, the monitoring instrumentation is calibrated in conjunction with the specific catheter prior to use. A traditional method for calibrating the monitoring instrumentation involves immersing the catheter sensor component in a calibration solution that has been pre-calibrated to a given set of values, confirmed using a separate calibration instrument such as a blood gas analyzer. If the catheter is subject to the above-described ETO sterilization and packaging process, the analyte sensing material of the sensor is completely dried and is not in proper chemical balance to carry out the monitoring process. Thus, the sensor must be hydrated and calibrated prior to use. If the traditional calibration method described above is carried out, the catheter is exposed and may be contaminated. It is also undesirable for a user to maintain a blood gas analyzer (BGA) for confirming the calibration of a blood gas catheter. Thus, it would be highly desirable to be able to supply a user with a sterile calibration solution and a procedure for using that solution to achieve more than one pre-determined calibration value that can be routinely applied without the requirement for confirming the calibration values in a blood gas analyzer. Further, it would be desirable if: a) the pH of this calibration solution in its packaged form be non-deleterious to the a sensor component stored in the solution; b) the calibration solution was buffered to offset any environmental contaminants that might alter the pH; and, c) if the pH could be brought within the desired range of pH within a reasonable period of time such that the user is not required to wait an inordinate amount of time before commencing use of the blood gas catheter. It would be further advantageous if the calibration solution could be used for hydrating, as well as calibrating, the sensor component of the blood gas catheter.
The package, calibration solution, packaging, and calibration method in the present invention overcomes these and other problems in the prior art.